1. Field of the Invention
The present invention relates to a rotary damper and an image forming apparatus.
2. Discussion of the Background
A technique has been conventionally known in which an anti-vibration rubber is provided between gears in a driving device that drivingly rotates a photoreceptor drum used in an electrophotographic copier to prevent transmission of vibration to the photoreceptor drum (see, for example, Japanese Unexamined Patent Application Publication No. 2002-174932).
A technique has also been known in which a flow rate of a viscous fluid is changed to keep a rotational vibration damping constant the same between low and high revolution times (see for example, Japanese Unexamined Patent Application Publication No. 2001-099231).
In an image forming apparatus of the Japanese Unexamined Patent Application Publication No. 2002-174932, the vibration is absorbed by the elastic deformation of the anti-vibration rubber and thus is prevented from being transmitted to the photoreceptor drum.
However, if the elastic coefficient of the anti-vibration rubber changes over time in accordance with a used period, or in accordance with a change in the surrounding temperature, the deformation amount value of the anti-vibration rubber changes in accordance with the used period or the surrounding temperature. Thus, the vibration damping effect cannot be stably obtained. As a result, the transmission of the vibration to the photoreceptor drum cannot be favorably prevented, and periodical unevenness occurs in images to be transferred onto a recording medium.
Thus, an object of the present invention is to provide a rotary damper that can efficiently prevent the transmission of the vibration regardless of the used environment